The goal of this project is to elucidate the role of the choroid plexuses, ependyma, and arachnoid membranes in a) the secretion of the cerebrospinal fluid (csf), and b) the maintenance of the "blood-cerebrospinal fluid barrier". In vitro preparations of the choroid plexus, ependyma and arachnoid membranes will be used to investigate 1) cellular and molecular mechanisms of csf secretion, 2) mechanisms of ion (e.g. K and I) transport between csf and blood, 3) exchange of drugs and solutes between the fluid compartments of the brain, and 4) the role of cilia in the mixing of the csf. The methods to be used include radioactive tracer techniques to measure fluxes across membranes, electrophysiological techniques to measure the electrical properties of membranes, fluorescence techniques to probe membrane structure and transport, and transducer techniques to measure volume flow across membranes. Cilia will be studied by a combination of optical, electrical and tracer techniques.